Genetics after Mendel

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Transcript of Genetics after Mendel

CodominanceOccurs when two alleles are equally

dominantThe heterozygous condition results in both phenotypes being equally expressed.Incomplete dominanceOccurs when one allele influences the second allele.The heterozygous condition produces an intermediate phenotypeGenetics after MendelMultiple AllelismMore than two different alleles exist for a particular geneResults in a larger number of possible genotypic combinations and a greater variety of phenotypesLinkageSex-linkageHuman X chromosome is large and contains many genes while the Y chromosome contains only a few.Complex patterns of inheritanceGenetics after MendelExample: Red-green colourblindnessAlleles of different genes found on the same chromosomeLet's take a closer look...Example: Red and white horses / cowsList the genotype and phenotype probabilities of the offspring resulting from a white horse crossed with a red horse.Example: White and red snapdragonsList the genotype and phenotype ratios for the offspring between a red snapdragon crossed with a white snapdragon.Example: Human blood types (A, B, O)100% Roan horsesExampleLinked genes do not separate from each other unless crossing over occurs.1 normal female: 1 carrier female : 1 normal male: 1 colour-blind malePhenotype Ratio:3rd phenotype== diversity=

linked genesDo not assort independentlySo only 1 allele for the disorder results in the male being affectedNotice there are no alleles on the Y chromosomeExample: HemophiliaPhenotype Ratio:1 carrier female: 1 hemophiliac female: 1 normal male: 1 hemophiliac maleLet's take a look at the way we write the alleles...A woman with Type O blood claims a man with Type AB blood is the father of her Type O blood son. Is this possible? Explain your reasoning using a Punnett square.Example: Red-green colourblindnessColourblindness is a recessive X-linked disorder.What are the allele combinations present in the gametes?